Video telephony (VT) involves the real-time communication of packets carrying audio and video data. Each VT device includes a video encoder that obtains video from a video capture device, such as a video camera or video archive, and generates packets of video data (“video packets”). Similarly, an audio encoder in each VT device obtains audio from an audio capture device, such as a microphone or speech synthesizer, and generates packets of audio data (“audio packets”). The video packets and audio packets are placed in a radio link protocol (RLP) queue. A medium access control (MAC) layer module generates medium access control (MAC) layer packets from the contents of the RLP queue. The MAC layer packets are converted to physical (PHY) layer packets for transmission across a communication channel to another VT device.
In mobile VT applications, a VT device receives the physical layer packets via a wireless forward link (FL) (or “downlink”) from a base station to the VT device, which may be a mobile wireless terminal such as a cellular radiotelephone. A VT device transmits the PHY layer packets via a wireless reverse link (RL) (or “uplink”) from the VT device to the base station. Each VT device includes PHY and MAC layers to convert the received PHY and MAC layer packets and reassemble the packet payloads into audio packets and video packets. A video decoder within the VT device decodes the video data for presentation to a user via a display device. An audio decoder within the VT device decodes the audio data for presentation via an audio speaker. Likewise, a VT device may include a video encoder and audio encoder to encode video and audio, respectively, for transmission to another VT device.
Video data errors may occur during transmission of video packets from the video encoder to the video decoder. For example, the error may occur during transmission on the RL (from the video encoder to the base station), at the base station, or during transmission on the FL (from the base station to the video decoder). Errors can undermine the visual quality of the video presented to a user. However, a variety of error correction or concealment techniques can be applied when errors are detected.